docs: def iter_annotation_values(graph, annotation: str) -> Iterable[str]:
      """Iterate over all of the values for an annotation used in the graph.
  
      :param pybel.BELGraph graph: A BEL graph
      :param str annotation: The annotation to grab
      """
      return (
          value
          for _, _, data in graph.edges(data=True)
          if edge_has_annotation(data, annotation)
          for value in data[ANNOTATIONS][annotation]
      )